1. Field of the Invention
The invention generally relates to BiCMOS (bipolar complimentary metal oxide semiconductor) technologies, and more particularly to a bipolar transistor device using SOI (semiconductor-on-insulator) wafers.
2. Description of the Related Art
Conventional CMOS (complimentary metal oxide semiconductor) technologies using single crystal silicon as an intrinsic base in an SOI structure are described in U.S. Pat. No. 5,118,634, issued to Neudeck et al. on Jun. 2, 1992 and Burghartz, J. N. et al., “SOI Bipolar Structure and the Fabrication Processes For Same,” IBM Technical Disclosure Bulletin, Vol. 35, No. 6, pp. 10-13, November 1992, the complete disclosures of which, in their entireties, are herein incorporated by reference.
Other conventional HBT (heterojunction bipolar) devices utilize a LTE (low temperature epitaxy) SiGe (Silicon Germanium) base grown on silicon bounded by a STI (shallow trench isolation) region. Characteristics of these devices include a single-crystalline SiGe intrinsic base and a polycrystalline extrinsic base consisting of polysilicon over the STI region, which renders the resulting NPN (or PNP) geometry non-planar, and in fact quite bumpy. Also, there is a transitional faceted region disposed in between the intrinsic and extrinsic bases. However, this link region is highly resistive, which adversely impacts device performance. Moreover, for CMOS designers there remains a big challenge in optimizing the photolithography processes for these devices when the devices are scaled down.
Neudeck teaches a vertical bipolar transistor using a single crystal extrinsic base contact to reduce the base resistance. Specifically, Neudeck teaches that the extrinsic base layer and insulator layers are over the substrate layer. Similarly, Burghartz teaches single crystal silicon as an extrinsic base in a SOI structure. Moreover, Burghartz teaches that the extrinsic base is on the insulator layer (such as SiO2), which is then configured on the substrate (e.g., a Si substrate). However, neither Neudeck, Burghartz, nor any of the other conventional devices teach a bipolar transistor having a single crystal extrinsic base and isolation regions formed in the substrate.
While, these devices were sufficient for the purposes they were designed, they do not provide optimum configurations for reducing the base resistance in the device. In addition, forming an isolation layer in Si substrates has been shown to be the most dominant approach in manufacturing due to the process simplicity. Therefore, due to the limitations of the conventional devices, there is a need for a practical and simple device and methodology that integrates SiGe HBTs with epitaxial extrinsic bases on SIMOX (separation by implanted oxygen) substrates and which overcomes the deficiencies of the conventional devices and methodologies.